Salivary C-Reactive Protein: A Non-Invasive Alternative to Serum CRP in Pediatric Acute Appendicitis

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Abstract
Background: The aim of this study was to evaluate the diagnostic potential of salivary C-reactive protein (CRP) as a non-invasive biomarker for acute appendicitis in children and to compare its levels with those found in blood. Methods: Salivary and serum CRP levels were measured in patients with histologically confirmed acute appendicitis (n = 46) and a control group with non-specific abdominal pain (n = 43). Diagnostic performance was evaluated using receiver-operating characteristic analysis, while the agreement between salivary and serum CRP levels was evaluated using Spearman’s correlation and the Bland–Altman method. Results: Salivary CRP levels were significantly elevated in children with acute appendicitis than in controls (median 35.7 vs. 1.1 mg/L, p < 0.001), closely mirroring serum CRP trends (median 44.3 mg/L vs. 1.1 mg/L, p < 0.001). Moreover, they demonstrated excellent discriminatory power (Area Under the Curve; AUC = 0.97; 91.3% sensitivity, 95.4% specificity at the optimal cut-off of 6.95 mg/L), comparable to that of serum CRP (AUC = 0.98; 89.1% sensitivity and 95.4% specificity at 10.3 mg/L cut-off). Levels of CRP in serum and saliva were strongly correlated (Spearman’s ρ = 0.963, p < 0.001) and overall showed good agreement on Bland–Altman. Although larger discrepancies (>10 mg/L) occurred in 29% of cases, there was no consistent bias favoring either the salivary or serum CRP measurements. Conclusions: Salivary CRP is a promising non-invasive biomarker for diagnosing acute appendicitis in children, demonstrating diagnostic performance closely comparable to that of serum CRP and acceptable agreement between the two measures. This method may reduce the need for invasive blood sampling and streamline early evaluation in pediatric emergency settings.

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